We consider the reaction e − e − → W − W − mediated by possible heavy neutrino exchange at future LINAC energies of s ⪢ 2mw. This reaction is sensitive to CP phases of the neutrino mixing matrices, even at the level of Born amplitudes. Certain integrated cross-sections are shown to have the power to resolve the CP phases when the experimental configurations are varied. Asymmetries sensitive to CP violation (involving initial QED phases) for e − e − and e + e + reactions are constructed and their consequences considered.